The recovery of resources, such as natural gas or oil, from an underground formation typically entails drilling a wellbore to the formation while circulating a drilling fluid, such as a water-based or oil-based drilling mud, within the wellbore. The drilling fluid flows down through the drill pipe (sometimes called a “drill string”), exits the pipe at a location adjacent the drill bit and then flows up through an annulus formed between the outside of the pipe and the wellbore wall. Circulation of the drilling fluid lubricates the drill bit and removes cuttings from the wellbore.
A problem that has been encountered in such a resource recovery process is loss of the drilling fluid to the underground formation during circulation of the fluid in the wellbore (a problem sometimes referred to as “lost circulation”). Drilling fluids may be lost to the underground formation (instead of circulating back up the wellbore) for a variety of reasons, such as, for example, the natural porosity of formation. Lost circulation is problematic for several reasons, including, for example, the high cost of replacing lost drilling fluids and the need to interrupt drilling until a problem resulting from lost circulation (such as breakage of the drill bit) is solved.
To address this problem, “lost circulation materials” (“LCMs”), are sometimes injected into the wellbore in an attempt to seal the pores of the porous underground formation. A common LCM is cement. Cement as an LCM, however, has drawbacks. For example, cement is only of limited sealing effectiveness, is prone to cracking, typically requires a very long time, such as around 24 hours, to cure, is typically of a viscosity that does not allow it to be squeezed into cracks in an underground formation, and needs to remain immobile in order to cure.
As a result, synthetic polymers, such as polyurethanes, have also been proposed for use as an LCM. As an LCM, polyurethanes have, however, also been difficult to implement. For example, many previous polyurethane-forming compositions have had an unacceptably short pot-life (which refers to the amount of time in which the combination of an active-hydrogen functional component, such as a polyol, and an isocyanate-functional component remains pumpable). As a result, complicated and cumbersome equipment options have been proposed to keep the reactive components separated during injection into the wellbore.
As an alternative, the use of blocked polyisocyanates to form a polyurethane LCM has also been proposed. Blocked polyisocyanates, however, require removal of the blocking agent in order for the isocyanate groups to react with an active-hydrogen functional component. When a liquid system is contained under pressure, as is the case in an LCM application, it is difficult, if not impossible, to remove the blocking agent. In addition, blocked polyisocyanate resins are usually very high in viscosity. As a result, they are very difficult to pump down the well bore without the use of solvents and/or plasticizers, which can be undesirable.
As a result, it would be desirable to provide improved methods of treating a well bore within an underground formation using a treatment composition that overcomes at least some of the foregoing problems.